The invention relates to a bistable electromagnetic actuating device, an armature assembly for an electromagnetic actuating device and a camshaft adjustment device.
DE 201 14 466 U1 shows a bistable electromagnetic actuating device for use for example in the camshaft adjustment devices described in DE 20 2009 011 804 U1. The known bistable electromagnetic actuating device is distinguished in that permanent magnet means are provided on an actuating element, which comprise two pole discs and an axially magnetised permanent magnet ring located therebetween. The permanent magnet means interact with a stationary core region, generating an attractive force together, permanent magnet means and core region being located opposite one another in a core-region-side end position. In this end position, a compression spring loading the actuating element with force away from the core region is maximally prestressed. In order to then overcome the retaining force of the permanent magnet means, a stationary coil apparatus is powered, wherein upon overcoming the adhesive force, the actuating element is additionally accelerated by the compression spring in the direction of the opposite end position, in which the piston-like actuating element engages with an end-side engagement region into the control groove of a cam of an internal combustion engine.
The known bistable electromagnetic actuating device has proven itself. However, the comparatively small travel ranges of the actuating element, in which the actuating element (permanent magnet armature) can move independently and without external influence into the core-region-side end position thereof, are found to be disadvantageous.
In the unpowered state of the coil apparatus, the permanent magnet means show a hyperbolic force-travel curve, in which, close to the core-region-side end position, the magnetic force rises steeply, but conversely falls quickly with increasing travel.
This is disadvantageous for spring-assisted bistable actuating devices, as only a small part of the available magnetic work can be used to prestress the spring, i.e. the travel range, in which sufficient permanent magnetic force is available in order to independently pull the actuating element provided with permanent magnet means back to the core-region-side end position is very narrow. Thus, in the case of known electromagnetic actuating devices, compression springs with very steep force-path characteristics must be used, in order to return the actuating element in the direction of the core-region-side travel initial position. There are also demands for an ever shorter travel time of the actuating element in the direction of the travel end position facing away from the core region. The previously mentioned travel time is particularly critical in the case of actuating devices for use in camshaft adjustment devices, as a fast control-groove engagement is decisively important.
An electromagnetic actuating device with an actuating element movable between two end positions is known from DE 10 2009 015 833 B4, which does not carry any permanent magnet means. The latter are arranged stationarily. In a retracted switching position, the end of a hollow cylinder of a flux-conducting body of the actuating device dips into an annular groove of a pole-body of the device.
DE 10 2006 059 188 A1 shows an electromagnetic actuating device, which has a permanent magnet on its actuating element. The permanent magnet runs parallel to the core region. A possible installation situation of bistable electromagnetic actuating devices is to be drawn from the published document in particular.
Starting from the previously mentioned prior art, the invention is based on the object of specifying an actuating device, which is optimised with regards to the travel time of the actuating element into the end position facing away from the core region and in which at the same time, a return of the actuating element having the permanent magnet means in the direction of the core-region-side end position acts at an earliest possible point in time, i.e. a travel force acts in the direction of the travel initial position at a comparatively large distance from the core region. Furthermore, the object consists in specifying a correspondingly optimised armature assembly and also a camshaft adjustment device with a correspondingly improved bistable electromagnetic actuating device.